Struct OffsetMapping 

pub struct OffsetMapping {
    pub transformations: Vec<Transformation>,
    /* private fields */
}

Offset mapping structure for tracking position changes during text filtering.

This structure maintains a list of all text transformations that occurred during character filtering, enabling accurate position mapping between filtered and original text.

Usage Pattern

1. Record transformations during filtering:

let mut mapping = OffsetMapping::new();
// When "㍑" → "リットル" transformation occurs:
mapping.add_transformation(Transformation::new(6, 9, 2, 14));

2. Correct positions from filtered to original:

let original_pos = mapping.correct_offset(filtered_pos, text.len());

Multi-Filter Support

When multiple character filters are applied, their mappings are composed:

let combined_mapping = mapping1.compose(mapping2);

This ensures accurate position tracking through complex filter chains.

Fields

transformations: Vec<Transformation>

List of transformations applied to the text

Implementations

impl OffsetMapping

pub fn new() -> Self

pub fn with_transformations(transformations: Vec<Transformation>) -> Self

pub fn add_transformation(&mut self, transformation: Transformation)

Add a transformation to the mapping

pub fn is_empty(&self) -> bool

Check if this mapping is empty (no transformations)

pub fn correct_offset(&self, offset: usize, text_len: usize) -> usize

Correct a position in filtered text to the corresponding position in original text.

This method maps a byte position in the filtered text back to the corresponding byte position in the original text, accounting for all recorded transformations.

Arguments

• offset - Byte position in the filtered text
• text_len - Length of the filtered text (used for boundary validation)

Returns

The corresponding byte position in the original text.

Algorithm

1. If no transformations exist, return the offset unchanged
2. Find the transformation whose filtered range contains the offset
3. Map the offset to the corresponding position in the original range
4. If offset is outside all transformation ranges, adjust by cumulative differences

Example

// For "１０㍑" → "10リットル" with transformations recorded
let mut mapping = OffsetMapping::new();
mapping.add_transformation(Transformation::new(6, 9, 2, 14));

// Position 2 in "10リットル" ("リットル" start)
let original_pos = mapping.correct_offset(2, 14); // returns 6
// This maps to position 6 in "１０㍑" ("㍑" start)

pub fn compose(self, other: OffsetMapping) -> OffsetMapping

Compose this mapping with another mapping (for chaining filters)

Trait Implementations

impl Clone for OffsetMapping

fn clone(&self) -> OffsetMapping

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for OffsetMapping

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for OffsetMapping

fn default() -> OffsetMapping

Returns the “default value” for a type.

impl PartialEq for OffsetMapping

fn eq(&self, other: &OffsetMapping) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for OffsetMapping